All Next Actions have a place and a time in which they get done.
You have stated that you can do your math homework "anywhere", but you failed to give us a time. Can you also do your homework at "anytime", or must it be done tonight after 9pm, or ???
If you can truly do your math homework "anywhere" and "anytime", then you must have a relatively open schedule and a relatively open calendar. Lucky you. In this case, your main problem is remembering to bring your tools with you. Under the 2-minute rule, you should simply tuck your tools into your bookbag and be done with it.
If your homework must get done today, then it goes on your calendar for today, with or without a set time (as you see fit).
If your homework must get done within a week, then it goes on your Projects list with a due date. There is no Next Action associated with this project in this case. The project migrates from your Projects List directly into your Calendar, circumventing the need to go onto your Next Actions Lists.
Each morning, when you plan your day, you need to look at all of the Projects and Next Actions in your system. Decide which ones you are going to do today, and put them on your calendar. Remember, the calendar is sacred ground. Anything you put on the calendar MUST GET DONE THAT DAY. You can always do more than what is on your calendar. That's what the @context lists are for, of course But if your homework is something that needs to be done today, then put it on your calendar.
Hope this helps,